This is a documentation of the routes, highways, parking requirements, or anything related to transportation in Houston. Roads and highways Houston has a hub-and-spoke freeway structure with multiple loops. The innermost is Interstate 610, forming approximately a loop around downtown. The roughly square "Loop-610" is quartered into "North Loop," "South Loop," "West Loop," and "East Loop." The roads of Beltway 8 and their freeway core, the Sam Houston Tollway, are the next loop, at a diameter of roughly 25 miles. A proposed highway project, State Highway 99 (The Grand Parkway), would form a third loop outside Houston, though some sections of this project have been controversial. As of June 2016, two portions of State Highway 99 have been completed: a 14.5-mile segment completed in April 2008 that runs from Interstate 10 in Mont Belvieu to Business State Highway 146 in Baytown, east of Houston; and a 71-mile segment completed between August 1994 and March 2016 that runs from Interstate 69/U.S. Highway 59 in Sugar Land, southwest of Houston, to Interstate 69/U.S. Highway 59 in New Caney, northeast of Houston. The next portions to be constructed are from the current terminus at Interstate 69/U.S. Highway 59 in Sugar Land to State Highway 288 in Brazoria County, and from the current terminus at Interstate 69/U.S. Highway 59 in New Caney to the current terminus at Interstate 10 in Mont Belvieu. Houston also lies along the route of the proposed Interstate 69 North American Free Trade Agreement (NAFTA) superhighway that will link Canada, the U.S. industrial mid-west, Texas, and Mexico. Mass transit The Metropolitan Transit Authority of Harris County, Texas, or METRO, provides public transportation in the form of buses, trolleys, and lift vans. METRO began running light rail service (METRORail) on January 1, 2004. Currently the track runs approximately 13 miles (20.8 km) from Downtown Houston to the Texas Medical Center and Reliant Park Southbound and to the Northline Mall Northbound. METRO operates an extensive park-and-ride bus system to serve many of Houston's outlying suburban areas. Most of the park-and-ride buses run in barrier-separated high-occupancy-vehicle (HOV) lanes that provide direct service from park-and-ride parking lots to major employment destinations. Prior to the opening of METRORail, Houston was the largest city in the United States without a rail transit system. Following a successful referendum held locally in 2003, METRO is currently in the beginning design phases of a 10-year expansion plan to add